1. Field of the Invention
The present invention relates to a high zoom-ratio zoom lens system, having a zoom ratio exceeding 13:1 for use in an SLR camera, and especially for use in a digital SLR camera.
2. Description of Related Art
A high zoom-ratio zoom lens system having a zoom ratio of approximately 10:1 and a focal length of 300 mm at the long focal length extremity is known, in the art, to have a six lens group arrangement, i.e., a positive lens group, a negative lens group, a positive lens group, a negative lens group, a positive lens group and a negative lens group, in this order from the object. Such known high zoom-ratio zoom lens systems are disclosed in Japanese Unexamined Patent Publication Nos. H11-174327, H04-186213, H04-186211 and H04-146407.
However, the high zoom-ratio zoom lens system disclosed in Japanese Unexamined Patent Publication No. H11-174327 has a focal length of 300 mm at the long focal length extremity, so that a sufficient high zoom ratio cannot be attained.
On the other hand, in the high zoom-ratio zoom lens systems disclosed in Japanese Unexamined Patent Publication Nos. H04-186213, H04-186211 and H04-146407, the telephoto side weighs in the optical design thereof; and, the high zoom-ratio zoom lens systems achieve a focal length of 350 mm at the long focal length extremity and an F-number of 5.6. However, the focal length at the short focal length extremity is approximately 35 mm; and, if an APS-C sized digital SLR camera is used, the angle-of-view thereof is only approximately 45°.